I hold that to be a “self-evident truth”. But if you want proof, the British police can always be relied on to provide it. In the latest incident they detained and questioned David Miranda at Heathrow airport on 18 August under schedule 7 of the 2000 anti-terrorism act.

Who is David Miranda?

Miranda is the partner of Glenn Greenwald, who has written a series of stories for the Guardian revealing mass surveillance programmes by the NSA. It was Greenwald who interviewed Edward Snowden and he continues to follow-up on all aspects of the story. Miranda was not, properly speaking, in the UK. He’d got off a flight from Berlin and was waiting for his flight home to Rio. He was questioned for nine hours about Greenwald’s activity as a journalist working on the NSA story. Before releasing Miranda, the police “confiscated” all his electronic kit: laptop, memory sticks, cell phone, DVDs and games consoles.

Schedule 7 of the Terrorism Act has been widely criticised for giving police broad powers under the guise of anti-terror legislation to stop and search individuals without prior authorisation or reasonable suspicion – setting it apart from other police powers.

Those stopped have no automatic right to legal advice and it is a criminal offence to refuse to co-operate with questioning under schedule 7, which critics say is a curtailment of the right to silence.

Miranda was not questioned about anything to do with terrorism. He was interrogated over his partner’s professional activity as a journalist. Therefore his detention was illegal. It really is as simple as that.

That this was a flagrant attempt to intimidate Glenn Greenwald goes without saying. It was also incredibly clumsy, so much so that an apology will probably be issued and the cracks papered over. But a clumsy warning is still a warning.